Bacterial motility and its modulation by chemical gradient stimuli are being used as a model system of motor function under control of sensory stimuli. The principal species being used are the gram negative species Salmonella and E. coli, and the gram positive species Bacillus subtilis. The energy vs. power characteristics of the motor are being studied using tethered cells and permeant cations and acids for measuring electrical and chemical potential components of protonmotive force. The reversibility of the motor has been found by us to be dependent on a critical protonmotive force level and we are attempting to determine the basis for this. The phenomenon of polymorphic transitions of the flagella during tumbling has been established and is being further studied. Using high-intensity dark-field microscopy and an intensifying vidicon camera, it is possible to record dynamic function of individual flagella; we are currently using this approach to study the synchrony (or lack thereof) of flagella on a single cell.